Core-satellite-structured magnetic nanozyme enables the ultrasensitive colorimetric detection of multiple drug residues on lateral flow immunoassay.

BACKGROUND: Excessive use of veterinary drugs causes severely environmental pollution and agricultural pollution, and poses great threat to human health. A simple method for the rapid, highly sensitive, and on-site monitoring of veterinary drug residues in complex samples remains lacking. RESULTS: In this study, we propose a catalytically enhanced colorimetric lateral flow immunoassay (LFA) based on a novel core-satellite-structured magnetic nanozyme (Fe-Au@Pt) that can simultaneously and quantitatively detect three common veterinary drugs, namely, gentamicin (GM), streptomycin (STR), and clenbuterol (CLE), within a short testing time (<30 min). The Fe-Au@Pt nanozyme was simply prepared through the self-assembly of numerous Au@Pt nanoparticles on a large Fe3O4 core via electrostatic adhesion, which exhibited the advantages of high peroxidase-like activity, strong magnetic responsiveness, and multiple catalytic sites. Under the dual-signal amplification effect of magnetic enrichment and catalytic enhancement, the proposed nanozyme-LFA allowed the multiplex detection of STR, CLE, and GM with detection limits of 10.1, 6.3, and 1.1 pg/mL, respectively. SIGNIFICANCE: The developed Fe-Au@Pt-LFA achieves direct, simultaneous, and accurate detection of three target drugs in food samples (honey, milk, and pork). The proposed assay shows great potential for application in the real-time monitoring of small-molecule pollutants in complex environment.

Low-triggering-potential electrochemiluminescence based on mental-organic frameworks encapsulation of ruthenium for synthetic cathinone detection by coupling photonic crystal light-scattering signal amplification of covalent-organic frameworks.

Developing effective electrochemiluminescence (ECL) platforms is always an essential concern in highly sensitive bioanalysis. In this work, a low-triggering-potential ECL sensor was designed for detecting synthetic cathinone 3,4-methylenedioxypyrovalerone (MDPV) based on a dual-signal amplification strategy. Initially, a probe was created by integrating Ruthenium into the hollow porphyrin-based MOF (PCN-222) structure to decrease the excitation potential and enhance ECL performance without external co-reaction accelerators. Additionally, for the first time, photonic crystals (PCs) assembled from covalent organic frameworks (COFs) were employed to amplify the ECL signal, thereby increasing the photon flux and the loading capacity of the ECL emitter to enhance sensitivity of the sensor. In the presence of the target MDPV, the aptamer labeled with Ferrocene (Fc) experienced conformational changes, causing Fc to approach the luminophore and resulting in ECL quenching. This effect was attributed to aptamer's conformational changes induced by the target, directly correlating with the target concentration. The constructed sensor showed good linearity with the target MDPV concentration, covering a dynamic range from 1.0 × 10-14 to 1.0 × 10-6 g/L and achieved an ultra-low detection limit of 4.79 × 10-15 g/L. This work employed dual amplification strategies to enhance ECL signals effectively, providing a novel method for developing highly responsive and bioactive sensors.

Combining WO3@AuNPs with Poly(amidoamine) Allows Sensitive Electrochemical Detection of DR1 Based on Dual Signal Amplification.

Down-regulator of transcription 1 (DR1) is considered as a biomarker of hashimoto's thyroiditis (HT), which is a risk factor for thyroid cancer. Here, a label-free electrochemical biosensor for DR1 detection was constructed based on polyamidoamine (PAMAM) polymer and the nanocomposite (WO3@AuNPs) composed of tungsten trioxide (WO3) and gold nanoparticles (AuNPs). WO3@AuNPs was obtained by combining monolayer WO3 nanosheets, which has high conductivity, and AuNPs. The modification of WO3@AuNPs can not only increase the conductivity of the electrode but also provide more active sites for signaling units, thus greatly improve the sensitivity of the sensor. The polymer PAMAM is biocompatible and non-immunogenic, and its end functional group can bind to the target molecules, providing them with more binding sites and thus improving the sensitivity of the sensor. Under optimal conditions, the label-free biosensor showed a good linear relationship between the logarithm of DR1 concentration and the impedance in the range of 10 fg ⋅ mL-1 to 100 ng ⋅ mL-1, with a detection limit as low as 0.3 fg ⋅ mL-1. Besides, this label-free electrochemical platform exhibited satisfactory selectivity and anti-interference capability in human serum samples. Therefore, this method has considerable potential in clinical detection of DR1.

Simple fabrication of electrochemical sensor based on integration of dual signal amplification by the supporting electrode and modified nanochannel array for direct and sensitive detection of vitamin B2.

Development of simple and reliable sensor for detecting vitamin content is of great significance for guiding human nutrition metabolism, overseeing the quality of food or drugs, and advancing the treatment of related diseases. In this work, a simple electrochemical sensor was conveniently fabricated by modification a carbon electrode with vertically-ordered mesoporous silica film (VMSF), enabling highly sensitive electrochemical detection of vitamin B2 (VB2) based on the dual enrichment of the analyte by the supporting electrode and nanochannels. The widely used glassy carbon electrode (GCE), was preactivated using simple electrochemical polarization, The resulting preactivated GCE (p-GCE) exhibited improved potential resolution ability and enhanced peak current of VB2. Stable modification of VMSF on p-GCE (VMSF/p-GCE) was achieved without introducing another binding layer. The dual enrichment effect of the supporting p-GCE and nanochannels facilitated sensitive detection of VB2, with a linear concentration ranged from 20 nM to 7 µM and from 7 µM to 20 µM. The limit of detection (LOD), determined based on a signal-to-noise ratio of three (S/N = 3), was found to be 11 nM. The modification of ultra-small nanochannels of VMSF endowed VMSF/p-GCE with excellent anti-interference and anti-fouling performance, along with high stability. The constructed sensor demonstrated the capability to achieve direct electrochemical detection of VB2 in turbid samples including milk and leachate of compound vitamin B tablet without the need for complex sample pretreatment. The fabricated electrochemical can be easily regenerated and has high reusability. The advantages of simple preparation, high detection performance, and good regeneration endow the constructed electrochemical sensor with great potential for direct detection of small molecule in complex samples.

Hemin/G-quadruplex and AuNPs-MoS2 based novel dual signal amplification strategy for ultrasensitively sandwich-type electrochemical thrombin aptasensor.

In this work, a novel sandwich-type electrochemical aptasensor based on the dual signal amplification strategy of hemin/G-quadruplex and AuNPs-MoS2 was designed and constructed, which realized the highly sensitive and specific detection of thrombin (TB). In this aptasensor, the 15-mer TB-binding aptamer (TBA-1) modified with thiol group was immobilized on the surface of AuNPs modified glassy carbon electrode (AuNPs/GCE) as capturing elements. Another thiol-modified 29-mer TB-binding aptamer (TBA-2) sequence containing G-quadruplex structure for hemin immobilization was designed. The formed hemin/G-quadruplex/TBA-2 sequence was further combined to the AuNPs decorated flower-like molybdenum disulfide (AuNPs-MoS2) composite surface via Au-S bonds, acting the role of reporter probe. In presence of the target TB, the sandwich-type electrochemical aptamer detection system could be formed properly. With the assistance of the dual signal amplification of AuNPs-MoS2 and hemin/G-quadruplex toward H2O2 reduction, the sandwich-type electrochemical aptasensor was successfully constructed for sensitive detection of TB. The results demonstrate that the fabricated aptasensor displays a wide linear range of 1.0 × 10-6 âˆ¼ 10.0 nM with a low detection limit of 0.34 fM. This proposed aptasensor shows potential application in the detection of TB content in real biological samples with high sensitivity, selectivity, and reliability.

Ultrasensitive electrochemiluminescence sensor for the detection of synthetic cannabinoids based on perovskite as coreaction accelerator and light-scattering effects of photonic crystals.

As is common knowledge, a strong electrochemiluminescence (ECL) signal is required to ensure the high sensitivity of trace target detection. Here, a dual signal amplification strategy by integrating of perovskite and photonic crystal was fabricated for quantitative synthetic cannabinoids (AB-PINACA) detection based on Zr-connected PTCA and TCPP (PTCA-TCPP) with excellent ECL performance as luminophores. On the one hand, the co-reaction accelerator perovskite (LaCoO3) improved the effective electroactive area of the electrode and promoted the decomposition of K2S2O8, resulting in a stronger ECL signal value. On the other hand, polystyrene inverse opal (PIOPCs) formed after the swelling of PS microspheres not only taken advantage of the light scattering effect and excellent catalytic property of photonic crystals to amplify the ECL signal, but also could be used as a binder to fix LaCoO3 and PTCA-TCPP on the electrode surface to generate unprecedented ECL response and stable ECL signals. Subsequently, the detection substance AB-PINACA was loaded on the electrode surface via the amide bond with the luminophores PTCA-TCPP, thus quenching the ECL signal, so as to realize the sensitive detection of synthetic cannabinoids. Under the optimal conditions, the proposed sensor achieved highly sensitive AB-PINACA detection with a dynamic range from 1.0 × 10-12 to 1.0 × 10-3 g/L and the detection limit was 1.1 × 10-13 g/L, which had great application potential in the detection of synthetic cannabinoids.

"Lollipop" particle counting immunoassay based on antigen-powered CRISPR-Cas12a dual signal amplification for the sensitive detection of deoxynivalenol in the environment and food samples.

Deoxynivalenol is one of the most widely distributed mycotoxins in cereals and poses tremendous threats to the agricultural environment and public health. Therefore, it is particularly important to develop sensitive and interference-resistant deoxynivalenol analysis methods. Here, we establish a "Lollipop" particle counting immunoassay (LPCI) based on antigen-powered CRISPR-Cas12a dual signal amplification. LPCI achieves high sensitivity and accuracy through antigen-powered CRISPR-Cas dual signal amplification combined with particle counting immunoassay. This strategy not only broadens the applicability of the CRISPR-Cas system in the field of non-nucleic acid target detection; it also improves the sensitivity of particle counting immunoassay. The introduction of a polystyrene "lollipop" immunoassay carrier further enables efficiently simultaneous pre-treatment of multiple samples and overcomes complex matrix interference in real samples. The linear detection range of LPCI for deoxynivalenol was 0.1-500 ng/mL with a detection limit of 0.061 ng/mL. The platform greatly broadens the scope of the CRISPR-Cas sensor for the detection of non-nucleic acid hazards in the environment and food samples.

A label-free electrochemical immunosensor based on PtCoCu PNPs/NB-rGO as a dual signal amplification platform for sensitive detection of ß-Amyloid1-42.

In this work, a label-free electrochemical immunosensor based on popcorn-shaped PtCoCu nanoparticles supported on N- and B-codoped reduced graphene oxide (PtCoCu PNPs/NB-rGO) was constructed to sensitively detect concentration level of ß-Amyloid1-42 oligomers (Aß). The PtCoCu PNPs exhibits excellent catalytic ability due to its popcorn structure which improves the specific surface area and porosity, resulting in more active sites being exposed and fast transport paths for ion/electron. NB-rGO with large surface area and unique pleated structure could disperse PtCoCu PNPs through electrostatic adsorption and formation of d-p dative bonds between the metal ion and pyridinic N of NB-rGO. In addition, the doping of B atoms enhances the catalytic ability of GO enormously and achieves further signal amplification. Besides, both PtCoCu PNPs and NB-rGO are able to fix abundant antibodies through M(Pt, Co, Cu)-N bonds and amide bonds respectively without any other complex processing procedures such as carboxylation, ect. The designed platform achieved the dual amplification of electrocatalytic signal and effectively immobilization of antibodies. Under the optimum conditions, the designed electrochemical immunosensor presented wide linear rang (50.0 fg/mL âˆ¼ 100 ng/mL) and low detection limits (3.5 fg/mL). The results demonstrated that the prepared immunosensor will be promising in sensitive detection of AD biomarkers.

Dual signal amplified electrochemical aptasensor based on PEI-functionalized GO and ROP for highly sensitive detection of cTnI.

Cardiac troponin I (cTnI) is considered as the gold standard for the diagnosis of acute myocardial infarction (AMI) because of its excellent specificity and sensitivity. Herein, a novel aptasensor based on the dual signal amplification strategy of Polyethyleneimine functionalized Graphene oxide (GO) and ring-opening polymerization (ROP) for the first time was successfully constructed to achieve high sensitivity detection of cTnI. Briefly, cTnI-aptamer 1 (Apt1) was immobilized on the surface of gold electrode by self-assembly of Au-S bonds to specifically capture cTnI. After specific recognition of cTnI, Apt2 coated PEI-functionalized GO composites acted as macroinitiators for the subsequent ROP reaction. Next, α-amino acid-N-carboxylic acid anhydride ferrocene derivatives (NCA-Fc), the monomer for ROP reaction, was added to the electrode surface. The combined application of PEI-functionalized GO and NCA-Fc better achieves the high sensitivity and signal amplification of the aptasensor. Under optimal conditions, the aptasensor exhibited a wide linear range of 10 fg mL-1 to 10 ng mL-1 and the limit of detection was 3.78 fg mL-1. Moreover, this method displayed the advantages of good selectivity, simple operation and excellent stability. Meanwhile, the aptasensor had good accuracy and applicability even in real serum samples analysis, demonstrating its considerable application potential in biomedical assays.

Highly sensitive fluorescence detection of tobacco mosaic virus RNA based on polysaccharide and ARGET ATRP double signal amplification.

Plant diseases caused by tobacco mosaic viruses (TMV) reduce the yield and quality of crops and cause significant losses. Early detection and prevention of TMV has important value of research and reality. Herein, a fluorescent biosensor was constructed for highly sensitive detection of TMV RNA (tRNA) based on the principle of base complementary pairing, polysaccharides and atom transfer radical polymerization by electron transfer activated regeneration catalysts (ARGET ATRP) as double signal amplification strategy. The 5'-end sulfhydrylated hairpin capture probe (hDNA) was first immobilized on amino magnetic beads (MBs) by a cross-linking agent, which specifically recognizes tRNA. Then, chitosan binds to BIBB, providing numerous active sites for fluorescent monomer polymerization, which successfully significantly amplifying the fluorescent signal. Under optimal experimental conditions, the proposed fluorescent biosensor for the detection of tRNA has a wide detection range from 0.1 pM to 10 nM (R2 = 0.998) with a limit of detection (LOD) as low as 1.14 fM. In addition, the fluorescent biosensor showed satisfactory applicability for the qualitative and quantitative analysis of tRNA in real samples, thereby demonstrating the potential in the field of viral RNA detection.

Development of a Nafion-MWCNTs and in-situ generated Au nanopopcorns dual-amplification electrochemical aptasensor for ultrasensitive detection of OTA.

Trace detection of ochratoxin A (OTA) in foods is essential to mitigate risks to human health. Herein, a label-free electrochemical (EC) aptasensor based on dual-signal amplification of Nafion dispersed multi-walled carbon nanotubes (Nafion-MWCNTs) and Au nanopopcorns was developed for ultrasensitive detection of OTA. Nafion solution prevented the leaching of MWCNTs, and the Nafion-MWCNTs modified screen-printed carbon electrode (SPCE) acted as the sensing substrate which facilitated the uniform distribution of the electrodeposited Au nanopopcorns. The in-situ generated Au nanopopcorns could not only load a large amount of aptamers for specific identification of OTA, but also promote the electron transfer of the sensing platform. The incorporation of Nafion-MWCNTs and Au nanopopcorns realized dual-amplification of the aptasensor due to the enhanced conductivity and the increased electroactive surface area of the electrode. The modified electrodes were characterized through scanning electron microscopy, X-ray photoelectron spectroscopy and EC evaluation. Under optimal conditions, the electrochemical impedance spectroscopy (EIS) was measured for the determination of OTA. The as-fabricated Au nanopopcorns/Nafion-MWCNTs impedimetric aptasensor displayed excellent sensitivity with a detection limit as low as 1 pg/mL and a wide linear range of 1 pg/mL-10 ng/mL for OTA. Practical application of the aptasensor in the spiked malt samples achieved satisfactory recoveries of 89.82-95.65 %, which was also successfully verified to detect OTA in eleven batches of actual malt samples collected from the local market. The creative aptasensor is simple, cost-effective, sensitive, and accurate, showing great promise for on-site monitoring of other trace contaminants in foods by simply replacing the aptamers.

Isolation of Bacteria Aptamers with Non-SELEX for the Development of a Highly Sensitive Colorimetric Assay Based on Dual Signal Amplification.

In this work, an aptamer against Escherichia coli is isolated via non-SELEX, which executes efficient selection by employing repetitive cycles of centrifugation-based partitioning, and the binding site of the aptamer on E. coli cell surfaces is inferred to be a membrane protein. Moreover, truncated sequence 2-17-2 with a higher affinity (Kd = 101.76 nM) is employed for highly sensitive colorimetric detection of bacteria based on the dual signal amplification strategy. When targets exist, the release of DNA 1 from the polymer activates a hybridization chain reaction (HCR) between DNA 1 and DNA 2, thereby inducing the aggregation of probe 1. Subsequently, DNA 3 dissociated from probe 1 as a linker DNA further assembles probe 2/3. In this system, two types of DNA@gold nanoparticles (AuNPs) coexist and successively aggregate AuNPs based on divergent triggering mechanisms. Under optimal conditions, the dual signal amplification strategy presents excellent sensitivity (10 CFU mL-1) and specificity, as well as the realization of real sample analysis.

Engineering the Signal Transduction between CdTe and CdSe Quantum Dots for in Situ Ratiometric Photoelectrochemical Immunoassay of Cry1Ab Protein.

Controllable modulation of a response mode is extremely attracting to fabricate biosensor with programmable analytical performances. Here, we reported a proof-of-concept ratiometric photoelectrochemical (PEC) immunoassay of Cry1Ab protein based on the signal transduction regulation at the sensing interface. A sandwich-type PEC structure was designed so that gold nanorods sensitized quantum dots to fix primary antibody (Au NRs/QDs-Ab1) and methylene blue sensitized QDs to combine a second antibody (MB/QDs-Ab2), which served as photoelectric substrate and signal amplifier, respectively. Unlike common recognition element, such a sandwich-type PEC structure allowed for the in situ generation of two specific response signals. For analysis, Cry1Ab captured by Au NRs/QDs-Ab1 led to a decreased photocurrent (ICry1Ab), while the subsequently anchored MB/QDs-Ab2 produced another photocurrent (IMB). Noteworthy, by taking advantage of the different energy band gaps of QDs, varying locations of CdTe and CdSe QDs could realize different signal transduction strategies (i.e., Mode 1 and Mode 2). Investigations on data analysis of ICry1Ab and IMB via different routes demonstrated the superior analytical performances of ratiometry (Mode 1). Consequently, the ratiometric PEC immunosensor offered a linear range of 0.01-100 ng mL-1 with a detection limit of 1.4 pg mL-1. This work provides an efficient strategy for in situ collection of multiple photocurrents to design ratiometric PEC sensors.

CHA-based dual signal amplification immunofluorescence biosensor for ultrasensitive detection of dimethomorph.

Dimethomorph (DMM) is a widely used high-efficiency fungicide which poses unpredictable threats to the ecological environment and public health. It is significant to establish a sensitive and robust analytical method for DMM detection. Here, we fabricated a catalytic hairpin assembly (CHA) - based immunofluorescence (IMF) biosensor by using single-strand DNA and DMM antibody co-modified gold nanoparticles (H0-Ab-Au) as anti-interference probes and DMM antigen coated 96-well plate as the immune recognition element and CHA reaction vessel. Parameters relevant to AuNP probes preparation and CHA reaction environment were optimized. After optimization, the LOD of 0.002 ng/mL was calculated, with a linear correlation in inverse proportion to DMM concentration ranging from 0.01 ng/mL to 50 ng/mL. In addition, the developed biosensor was successfully applied to a variety of complex matrix samples, with satisfactory recoveries over a range of 86.74%-118.60%. Moreover, the detection results of IMF biosensor have a good correlation with liquid chromatography-tandem mass spectrometry (LC-MS/MS). Therefore, our proposed IMF biosensor exhibits ultra-high sensitivity and excellent specificity, as well as great potential for application to other hazards.

Electrochemical Sensor Nanoarchitectonics for Sensitive Detection of Uric Acid in Human Whole Blood Based on Screen-Printed Carbon Electrode Equipped with Vertically-Ordered Mesoporous Silica-Nanochannel Film.

Screen-printed carbon electrodes (SPCEs) bear great potential in the detection of biomarker in clinical samples with low sample consumption. However, modification of electrode surfaces to improve the anti-interference ability and sensitivity is highly desirable for direct electroanalysis of whole blood samples. Here, a reliable and miniaturized electrochemical sensor is demonstrated based on SPCE equipped with vertically-ordered mesoporous silica-nanochannel film (VMSF). To achieve stable binding of VMSF and improve the electrocatalytic performance, electrochemically reduced graphene oxide (ErGO) is applied as a conductive adhesion layer, that is in situ reduced from GO nanosheets during fast growth (less than 10 s) of amino groups modified VMSF (NH2-VMSF) using electrochemically assisted self-assembly (EASA). In comparison with bare SPCE, NH2-VMSF/ErGO/SPCE exhibits decreased oxidation potential of uric acid (UA) by 147 mV owing to significant electrocatalytic ability of ErGO. The dual signal amplification based on electrocatalysis of ErGO and enrichment of nanochannels leads to enhanced peak current by 3.9 times. Thus, the developed NH2-VMSF/ErGO/SPCE sensor enables sensitive detection of UA in the range from 0.5 µM to 180 µM with a low limit of detection (LOD, 129 nM, S/N = 3). Owing to good anti-fouling ability and high selectivity of the sensor, direct and rapid detection of UA in human whole blood is realized with very low sample consumption (50 µL).

Rolling circle amplification assisted dual signal amplification colorimetric biosensor for ultrasensitive detection of leukemia-derived exosomes.

Tumor-derived exosomes as a liquid biopsy marker hold great promising for the accurate tumor diagnosis. However, the visual exosomes detection method with high sensitivity and convenience is still a challenge and highly valuable in the clinical application. Herein, we fabricated a colorimetric biosensor that could visually detect leukemia-derived exosomes, and dual amplified the signal based on the rolling circle amplification (RCA) assisted platform. To avoid the interference of components in serum, trigger-aptamer complex was firstly modified on the magnetic beads (MBs) to recognize exosomes, and then release trigger probe to initiate RCA reaction. Therefore, the trigger probe could produce long repeated sequences and hybridized with numerous signal probe. After that, GNPs-HRP (HRP modified gold nanoparticles) bound with signal probe and induced dramatic color change of TMB to achieve the sensing of exosomes. Benefiting from the RCA assisted dual signal amplification, the presented method showed a limit of detection as low as 100 particles/µL. Moreover, this method exhibited good specificity to distinguish healthy and leukemia patients, suggesting its great potential for clinical diagnosis.

Enzyme-free and copper-free strategy based on cyclic click chemical-triggered hairpin stacking circuit for accurate detection of circulating microRNAs.

Accurate detection of circulating microRNAs (miRNAs) plays a vital role in the diagnosis of various diseases. However, enzyme-free amplification detection remains challenging. Here, we report an enzyme-free fluorescence resonance energy transfer assay termed "3C-TASK" (cyclic click chemical-triggered hairpin stacking kit) for the detection of circulating miRNA. In this strategy, the miRNA could initiate copper-free click chemical ligation reactions and the ligated products then trigger another hairpin stacking circuit. The first signal amplification was achieved through the recycling of the target miRNA in the click chemical ligation circuit, and the second signal amplification was realized through the recycling of ligated probes in a hairpin stacking circuit driven by thermodynamics. The two-step chain reaction event triggered by miRNAs was quantified by the fluorescence signal value so that accurate detection of target miRNA could be achieved. The 3C-TASK was easily controlled because no enzyme was involved in the entire procedure. Although simple, this strategy showed sensitivity with a detection limit of 8.63 pM and specificity for distinguishing miRNA sequences with single-base variations. In addition, the applicability of this method in complex biological samples was verified by detecting target miRNA in diluted plasma samples. Hence, our method achieved sensitive and specific detection of miRNA and may offer a new perspective for the broader application of enzyme-free chemical reaction and DNA circuits in biosensing.

Electrochemical immunosensor based on hollow porous Pt skin AgPt alloy/NGR as a dual signal amplification strategy for sensitive detection of Neuron-specific enolase.

Neuron-specific enolase (NSE) is a specific marker for small cell carcinoma (SCLC). Sandwich-type electrochemical immunosensors are powerful for biomarker analysis, and the electrocatalytic activity of the signal amplification platform and the performance of the substrate are critical to their sensitivity. In this work, N atom-doped graphene functionalized with hollow porous Pt-skin Ag-Pt alloy (HP-Ag/Pt/NGR) was designed as a dual signal amplifier. The hollow porous Pt skin structure improves the atomic utilization and the larger internal cavity spacing significantly increases the number of electroactive centers, thus exhibiting more extraordinary electrocatalytic activity and durability for H2O2 reduction. Using NGR with good catalytic activity as the support material of HP-Ag/Pt, the double amplification of the current signal is realized. For the substrate, polypyrrole-poly(3,4-ethylenedioxythiophene) (PPy-PEDOT) nanotubes were synthesized by a novel chemical polymerization route, which effectively increased the interfacial electron transfer rate. By coupling Au nanoparticles (Au NPs) with PPy-PEDOT, the immune activity of biomolecules is maintained and the conductivity is further enhanced. Under optimal conditions, the linear range was 50 fg mL-1 - 100 ng mL-1, and the limit of detection (LOD) was 18.5 fg mL-1. The results confirm that the developed immunosensor has great promise for the early clinical diagnosis of SCLC.

Dual Photoredox Catalysis Strategy for Enhanced Photopolymerization-Based Colorimetric Biodetection.

Catalytic redox reactions have been employed to enhance colorimetric biodetection signals in point-of-care diagnostic tests, while their time-sensitive visual readouts may increase the risk of false results. To address this issue, we developed a dual photocatalyst signal amplification strategy that can be controlled by a fixed light dose, achieving time-independent colorimetric biodetection in paper-based tests. In this method, target-associated methylene blue (MB+) photocatalytically amplifies the concentration of eosin Y by oxidizing deactivated eosin Y (EYH3-) under red light, followed by photopolymerization with eosin Y autocatalysis under green light to generate visible hydrogels. Using the insights from mechanistic studies on MB+-sensitized photo-oxidation of EYH3-, we improved the photocatalytic efficiency of MB+ by suppressing its degradation. Lastly, we characterized 100- to 500-fold enhancement in sensitivity obtained from MB+-specific eosin Y amplification, highlighting the advantages of using dual photocatalyst signal amplification.

Functionalized graphene oxide in situ initiated ring-opening polymerization for highly sensitive sensing of cytokeratin-19 fragment.

Improving the sensitivity of detection is crucial to monitor biomarker, assess toxicity, and track therapeutic agent. Herein, a sensitivity-improved immunosensor is reported for the first time via functionalized graphene oxide (GO) and a "grafting-to" ring-opening polymerization (ROP) dual signal amplification strategy. Through the ROP reaction using 2-[(4-ferrocenylbutoxy)methyl] oxirane (FcEpo) as the monomer, lots of electroactive tags are linked in situ from multiple initiation sites on the GO surface modified with ethanol amine (GO-ETA), thereby achieving high sensitivity even in the case of trace amounts of tumor markers. The utmost important factor for achieving this high sensitivity is to select functionalized GO as the initiator that contains a large number of repeated hydroxyl functional groups so as to trigger additional ROP reaction. Under the optimal conditions, the high sensitivity and applicability is demonstrated by the use of GO-ETA-mediated ROP-based immunosensor to detect non-small cell lung cancer (NSCLC)-specific biomarker down to 72.58 ag/mL (equivalent to ~6 molecules in a 5 µL sample). Furthermore, the satisfactory results for the determination of biomarkers in clinical serum samples highlighted that this immunosensor holds a huge potential in practical clinical application. This work described an electrochemical immunosensor for ultrasensitive detection of CYFRA 21-1 via the functionalized graphene oxide (GO) and a "grafting-to" ring-opening polymerization (ROP) dual signal amplification strategy, which hold the merits of high sensitivity, applicability, selectivity, efficiency, easy operation and environmental friendliness.